The ability to obtain accurate blood flow measurements by noninvasive radiographic methods would be of great benefit both in basic physiology research and in clinical medicine. With the development of modern digital radiography, this has become a realistic goal. The proposed project would develop, test and standardize a method for measuring blood flow by continuous digital filtration fluoroscopy, initially with the use of phantom models, where the flow can be controlled and measured directly. Tomographic fluoroscopy also will be used to aid in vessel localization and diameter measurements, essential to accurate flow measurement. Both intraarterial (aortic) and intravenous (superior vena caval) injection routes will be tested for measuring flow in selected arteries of mongrel dogs, using an electromagnetic flowmeter for control flow determinations. A particularly challenging and important vessel for measurement of flow is the portal vein. After validation of the methods in phantoms and in arteries, flow measurements will be made in both the hepatic arteries and portal veins of domestic swine. Attempts then will be made to correlate flow in these vessels with the opacification profile of the liver parenchyma as observed on digital filtration images, a step toward quantitating perfusion at the tissue level.